C++ PATCH for c++/49003 (DR 1207, use of 'this' in trailing return type)

[Jason Merrill <jason@redhat.com>]

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This patch adds support for use of 'this' (implicitly or explicitly) in 
the trailing-return-type of a member function.

Tested x86_64-pc-linux-gnu, applying to trunk.

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commit 8154a9854f1d5ff3407af1707d112899eb39f013
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jun 29 15:19:46 2011 -0400

    	DR 1207
    	PR c++/49003
    	* cp-tree.h (struct saved_scope): Add x_current_class_ptr,
    	x_current_class_ref.
    	(current_class_ptr, current_class_ref): Use them.
    	* decl.c (build_this_parm): Handle getting the class type.
    	* parser.c (cp_parser_late_return_type_opt): Set up 'this'
    	for use within the trailing return type.

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 55c88e3..ef25c97 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -953,6 +953,10 @@ struct GTY(()) saved_scope {
   struct cp_binding_level *x_previous_class_level;
   tree x_saved_tree;
 
+  /* Only used for uses of this in trailing return type.  */
+  tree x_current_class_ptr;
+  tree x_current_class_ref;
+
   int x_processing_template_decl;
   int x_processing_specialization;
   BOOL_BITFIELD x_processing_explicit_instantiation : 1;
@@ -1070,12 +1074,14 @@ struct GTY(()) language_function {
    PARM_DECL for the `this' pointer.  The current_class_ref is an
    expression for `*this'.  */
 
-#define current_class_ptr \
-  (cfun && cp_function_chain					\
-   ? cp_function_chain->x_current_class_ptr : NULL_TREE)
-#define current_class_ref \
-  ((cfun && cp_function_chain)                                  \
-   ? cp_function_chain->x_current_class_ref : NULL_TREE)
+#define current_class_ptr			\
+  (*(cfun && cp_function_chain			\
+     ? &cp_function_chain->x_current_class_ptr	\
+     : &scope_chain->x_current_class_ptr))
+#define current_class_ref			\
+  (*(cfun && cp_function_chain			\
+     ? &cp_function_chain->x_current_class_ref	\
+     : &scope_chain->x_current_class_ref))
 
 /* The EH_SPEC_BLOCK for the exception-specifiers for the current
    function, if any.  */
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index b8435a6..94d686d 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -7001,7 +7001,14 @@ build_this_parm (tree type, cp_cv_quals quals)
   tree parm;
   cp_cv_quals this_quals;
 
-  this_type = type_of_this_parm (type);
+  if (CLASS_TYPE_P (type))
+    {
+      this_type
+	= cp_build_qualified_type (type, quals & ~TYPE_QUAL_RESTRICT);
+      this_type = build_pointer_type (this_type);
+    }
+  else
+    this_type = type_of_this_parm (type);
   /* The `this' parameter is implicitly `const'; it cannot be
      assigned to.  */
   this_quals = (quals & TYPE_QUAL_RESTRICT) | TYPE_QUAL_CONST;
@@ -12675,6 +12682,7 @@ start_preparsed_function (tree decl1, tree attrs, int flags)
 
       cp_function_chain->x_current_class_ref
 	= cp_build_indirect_ref (t, RO_NULL, tf_warning_or_error);
+      /* Set this second to avoid shortcut in cp_build_indirect_ref.  */
       cp_function_chain->x_current_class_ptr = t;
 
       /* Constructors and destructors need to know whether they're "in
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index f1b7976..d79326d 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -1696,7 +1696,7 @@ static cp_cv_quals cp_parser_cv_qualifier_seq_opt
 static cp_virt_specifiers cp_parser_virt_specifier_seq_opt
   (cp_parser *);
 static tree cp_parser_late_return_type_opt
-  (cp_parser *);
+  (cp_parser *, cp_cv_quals);
 static tree cp_parser_declarator_id
   (cp_parser *, bool);
 static tree cp_parser_type_id
@@ -14968,7 +14968,7 @@ cp_parser_direct_declarator (cp_parser* parser,
 		  virt_specifiers = cp_parser_virt_specifier_seq_opt (parser);
 
 		  late_return
-		    = cp_parser_late_return_type_opt (parser);
+		    = cp_parser_late_return_type_opt (parser, cv_quals);
 
 		  /* Create the function-declarator.  */
 		  declarator = make_call_declarator (declarator,
@@ -15537,9 +15537,10 @@ cp_parser_virt_specifier_seq_opt (cp_parser* parser)
    Returns the type indicated by the type-id.  */
 
 static tree
-cp_parser_late_return_type_opt (cp_parser* parser)
+cp_parser_late_return_type_opt (cp_parser* parser, cp_cv_quals quals)
 {
   cp_token *token;
+  tree type;
 
   /* Peek at the next token.  */
   token = cp_lexer_peek_token (parser->lexer);
@@ -15550,7 +15551,23 @@ cp_parser_late_return_type_opt (cp_parser* parser)
   /* Consume the ->.  */
   cp_lexer_consume_token (parser->lexer);
 
-  return cp_parser_trailing_type_id (parser);
+  if (current_class_type)
+    {
+      /* DR 1207: 'this' is in scope in the trailing return type.  */
+      tree this_parm = build_this_parm (current_class_type, quals);
+      gcc_assert (current_class_ptr == NULL_TREE);
+      current_class_ref
+	= cp_build_indirect_ref (this_parm, RO_NULL, tf_warning_or_error);
+      /* Set this second to avoid shortcut in cp_build_indirect_ref.  */
+      current_class_ptr = this_parm;
+    }
+
+  type = cp_parser_trailing_type_id (parser);
+
+  if (current_class_type)
+    current_class_ptr = current_class_ref = NULL_TREE;
+
+  return type;
 }
 
 /* Parse a declarator-id.
diff --git a/gcc/testsuite/g++.dg/cpp0x/pr45908.C b/gcc/testsuite/g++.dg/cpp0x/pr45908.C
index 3a85088..45399b5 100644
--- a/gcc/testsuite/g++.dg/cpp0x/pr45908.C
+++ b/gcc/testsuite/g++.dg/cpp0x/pr45908.C
@@ -14,5 +14,5 @@ struct vector {
 class block {
     vector v;
     auto end() const -> decltype(v.begin())
-    { return v.begin(); } // { dg-error "could not convert" }
+    { return v.begin(); }
 };
diff --git a/gcc/testsuite/g++.dg/cpp0x/trailing6.C b/gcc/testsuite/g++.dg/cpp0x/trailing6.C
new file mode 100644
index 0000000..3476e90
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/trailing6.C
@@ -0,0 +1,6 @@
+// PR c++/49003
+// { dg-options -std=c++0x }
+
+struct A {
+    auto a() const -> decltype(this) { return this; }
+};